Orderly-micro-grooved pcd grinding wheel and method for making same

ABSTRACT

An orderly-micro-grooved PCD grinding wheel includes a wheel hub, a polycrystalline diamond (PCD) film, a number of micro-grinding units and a number of microgrooves. The PCD film is deposited on an outer circumferential surface of the wheel hub. The PCD film is processed by a water-jet guided laser device to form the microgrooves with high depth-width ratio and micro-grinding units with positive rake angles on the entire outer circumferential surface of the PCD film. An axial length of each micro-grinding unit and an axial length of each microgroove are equal to a thickness of the grinding wheel, respectively. The microgrooves are spaced apart by the micro-grinding units.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.16/677,635, filed on Nov. 7, 2019, now pending, which is a continuationof International Patent Application PCT/CN2019/090698, filed on Jun. 11,2019, and claims the benefit of priority from Chinese Patent ApplicationNo. 201810608183.3, filed on Jun. 13, 2018. The content of theaforementioned application, including any intervening amendmentsthereto, is incorporated herein by reference.

TECHNICAL FIELD

This application relates to a grinding wheel and preparation thereof,and more specifically to an orderly-micro-grooved PCD grinding wheel anda method for making the same.

BACKGROUND

Grinding has been widely applied in the precision machining due to thecharacteristics of high processing precision and good surface quality.However, in the traditional grinding process, abrasive grains areirregularly arranged on the working surface of the grinding wheel, andvary in geometrical shape and size, so that the abrasive grains oftencut the surface of the workpiece in a large negative rake angle duringgrinding, which will increase the grinding force ratio, accelerate theconversion of grinding energy into heat and raise the grindingtemperature, affecting the surface quality and grinding efficiency. Inaddition, the grinding wheel also has disadvantages of small chip spaceand low protrusion of abrasive grains, and the grains are easy to falloff, which may easily cause a blockage at the grinding wheel and producea local high temperature to burn the workpiece surface, and reduce theservice life of the grinding wheel.

Extensive researches have been performed to find a method for improvingthe grinding efficiency and service life of the grinding wheel. ChinesePublication No. 107962510A, titled “CVD diamond grinding wheel withordered surface micro-structure” put forward a method in which a diamondfilm is deposited on the outer circumferential surface of a grindingwheel hub by chemical vapor deposition, and a large number of staggeredand ordered microgrooves and grinding units with waist-type top surfaceare prepared on the outer circumferential surface of the whole diamondfilm by pulsed laser beam. This method improves the removal rate andgrinding efficiency of the surface material and increases the holdingforce of the grinding wheel hub for the grinding units, improving theservice life of the grinding wheel to a certain extent. However, thesingle grinding unit is still operated at a zero rake angle during thegrinding process, so that the grinding efficiency and the surfacequality cannot be further improved. Meanwhile, the circumferentialspacing of the orderly arranged grinding units reaches 1 mm, which willresult in a typical intermittent grinding, and the generated periodicvibrations by the grinding process may also affect the integrity of theground surface.

Further, in order to improve the integrity of the ground surface andachieve the grinding in a positive rake angle, Chinese Publication No.105728961A, titled “Method for manufacturing a new positive-rake anglediamond grinding tool based on pulse laser”, provides a method forpreparing positive rake angles of diamond abrasive grains by laser. Inthe method, the large single-layer diamond abrasive grains orderlyarranged on the working surface of the grinding wheel are ablated bylaser to obtain a point angle less than 90°, which enables grinding witha positive rake angle. The method effectively solves the problem thatabrasive grains of the conventional diamond grinding wheel cut thesurface of the workpiece in a large negative rake angle, which improvesthe processing efficiency and reduces the damage to the ground surface,improving the integrity of the ground surface. However, in the processof preparing large-sized diamond abrasive grains by laser, the highlaser ablation temperature will inevitably cause partial graphitizationof the diamond abrasive grains, affecting the positive rake anglecutting of the abrasive grains for the workpiece surface and reducingthe quality of the ground surface. At the same time, the singlelarge-sized diamond abrasive grain may fall off if it is subjected toexcessive or concentrated force, which may affect the grindingefficiency and even reduce the service life of the grinding wheel.

In order to further improve the quality of the ground surface and thegrinding efficiency, Chinese Patent Application Publication No.107243848A, titled “A spiral ordered fiber tool for positive rake angleprocessing and preparation method thereof”, discloses a method in whichthe matrix is prepared on the grinding wheel hub by pressing andsintering, and the ordered holes are processed on the matrix using adrilling bit. Then the fiber with positive rake angle is consolidated inthe small holes by the epoxy resin. The method enables cutting with apositive rake angle, and further improves the surface quality and theprocessing precision. However, since the fiber has a cross-sectionalsize of 0.8 mm×0.8 mm and the number of fibers per square centimeter onthe surface of the tool is only 14.26, the single fiber may have a largecutting depth, making it difficult to ensure the processing precision.Moreover, a rupture will occur if a single fiber is subjected to anexcessive or concentrated force, which may affect the service life ofthe grinding wheel. There are also great difficulties in the processthat all the fibers are inserted into the small holes one by one andconsolidated.

SUMMARY

The present disclosure provides a grinding wheel, comprising a wheelhub, a polycrystalline diamond (PCD) film, a plurality of micro-grindingunits and a plurality of microgrooves;

wherein an outer circumferential surface of the wheel hub is depositedwith the PCD film; the plurality of micro-grinding units and theplurality of microgrooves are orderly distributed on a whole outercircumferential surface of the PCD film; the plurality of micro-grindingunits form a part of the PCD film; and the plurality of microgrooves arespaced apart by the plurality of micro-grinding units;

each of the plurality of microgrooves and each of the plurality ofmicro-grinding units both have an axial length equal to a thickness ofthe grinding wheel; the micro-grinding units each comprise two sidesurfaces and an outer surface; the microgrooves each comprise two sidewalls that form one of the two side surfaces of two adjacentmicro-grinding units, respectively; and

the micro-grinding units each have an positive rake angle.

In some embodiments, the positive rake angle of each micro-grinding unitis 10°-40°, and the micro-grinding units each have a clearance angle of20°-50°.

In some embodiments, the micro-grinding units have substantially thesame geometric shapes and dimensions.

In some embodiments, a thickness of the PCD film is 1-2 mm.

In some embodiments, each micro-grinding unit has a circumferentialwidth of 80-150 μm and a radial height of 500-800 μm.

In some embodiments, each microgroove has a circumferential width of20-50 μm, a depth of 500-800 μm and a depth-width ratio of 10-40:1.

In some embodiments, the wheel hub is made of titanium alloy; and thewheel hub has a diameter of 100-200 mm and a thickness of 6-20 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view and a partial enlarged view showing a PCDgrinding wheel having a number of microgrooves and a number ofmicro-grinding units on its entire surface in accordance with anembodiment of the present invention;

FIG. 2 is a front view and a partial enlarged view showing the grindingwheel in contact with a surface of a workpiece in accordance with anembodiment of the present invention;

FIG. 3 is a perspective view showing a grinding wheel having a wheel hubon which a PCD film is deposited in accordance with an embodiment of thepresent invention; and

FIG. 4 is a schematic diagram showing the processing of the PCD film onthe wheel hub of the grinding wheel by a water-jet guided laser devicein accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Definitions

Term “reference plane” is a plane which is perpendicular to cuttingvelocity vector at a selected point on a cutting tool. Herein, thecutting tool may refer to abrasives, or particularly grinding units.

Term “cutting plane” is a plane which is tangent to the selected pointof the cutting tool where it is in contact with the surface of theworkpiece. The cutting plane is perpendicular to the reference plane.

Term “rake angle” is an angle between a rake face of the cutting tooland the reference plane. The rake angle may be categorized into threetypes: positive, zero or neutral, and negative. Herein, the cutting toolhas a positive rake angle.

Term “clearance angle” is an angle between a flank face of the cuttingtool and the cutting plane.

Term “substantially” herein refers to two or more elements are identicalto a great extent or degree, almost, but not absolutely the same.

Term “pickling” is a metal surface treatment used to remove impurities,such as stains, inorganic contaminants, rust or scale from ferrousmetals, copper, precious metals and aluminum alloys, and a solutioncalled pickle liquor, which usually contains acid, is used to remove thesurface impurities.

This application will be further illustrated with reference to theembodiments and drawings.

Referring to FIG. 1, a grinding wheel includes a wheel hub 1, apolycrystalline diamond (PCD) film 2, a plurality of micro-grindingunits 9 and a plurality of microgrooves 10. An outer circumferentialsurface of the wheel hub 1 is deposited with a PCD film 2. Themicro-grinding units 9 and the microgrooves 10 are orderly distributedon a whole outer circumferential surface of the PCD film. Themicrogrooves 10 are configured to hold chip and store grinding liquid.

Each microgroove 10 and each micro-grinding unit 9 both have an axiallength equal to a thickness of the grinding wheel. The microgrooves 10each have a circumferential width of 20-50 μm, a depth of 500-800 μm,and a depth-width ratio of 10-40:1. Since the arrangement of themicro-grinding units 9 and the microgrooves 10 are formed by subtractivemanufacturing or processing of the PCD film, the micro-grinding units 9are a part of the PCD film. The microgrooves 10 are spaced apart by themicro-grinding units 9 to create an ordered arrangement.

Particularly, referring to a partial enlarged view on the right side inFIG. 1, the micro-grinding units 9 each comprise two side surfaces 11,13 and an outer surface 14. The microgrooves 10 each comprise two sidewalls 11, 13 which form one of the two side surfaces 11, 13 of twoadjacent micro-grinding units, respectively. In other words, every twoadjacent micro-grinding units and the microgroove 10 between them sharethe side walls/surfaces 11, 13.

Referring to FIG. 2, particularly a partial enlarged view on the rightside, each micro-grinding unit 9 has a rake angle β, which is the anglebetween a rake face (i.e. side surface 13) of the micro-grinding unit 9and a reference plane π_(R). The rake angle β is positive, ranging from10° to 40°. In an embodiment, the rake angle β is 10°, 15°, 20°, 25°,30°, 35° or 40°, for the purpose of illustration.

Continuing to refer to FIG. 2, each micro-grinding unit 9 has aclearance angle α, which is the angle between a flank face (i.e. outersurface 14) of the micro-grinding unit 9 and a cutting plane π_(C). Thecutting plane is tangent to a selected point of the micro-grinding unit9 on a surface of a workpiece 12, as shown in FIG. 2. Here, the selectedpoint refers to the intersection of the rake face (i.e. side surface 13)and the flank face (i.e. outer surface 14), as seen from a front view ofthe grinding wheel. The reference plane π_(R) is perpendicular to thecutting plane π_(C). The clearance angle α of the micro-grinding unit 9is 20°-50°. In an embodiment, the clearance angle a is 20°, 25°, 30°,35°, 40°, 45° or 50°.

FIGS. 3-4 illustrate main procedures for the manufacturing of thegrinding wheel as shown in FIGS. 1-2.

Referring to FIG. 3, a layer of a PCD film 2 having a thickness of 1-2mm is deposited on a wheel hub 1 by a hot filament chemical vapordeposition (HFCVD) technique. Hot filament CVD is a method that has beenapplied to the deposition of diamond films and is available to personsskilled in the art. The thickness of the PCD film 2 may be 2 mm. Thewheel hub 1 may be made of titanium alloy, with a diameter of 100-200 mmand a thickness of 6-12 mm. Preferably, the diameter of the wheel hub is100 mm, and the thickness of the wheel hub is 12 mm. The outercircumferential surface of the PCD film 2 is polished by ion beampolishing to reach a surface roughness of 0.15-0.2 preferably 0.2 Theouter circumferential surface of the PCD film 2 is processed by awater-jet guided laser device, for example Laser MicroJet® IntegrationPackage (LMJ-iP) to form a number of microgrooves and micro-grindingunits on the entire surface of the PCD film 2. The process is areduction of material, that is subtractive manufacturing, so themicro-grinding units formed is a part of the PCD film. In an embodiment,the laser device is an Nd: YAG pulse laser with a wavelength of 532 nmand a focused spot diameter of 30-100 μm.

Referring to FIG. 4, the water-jet guided laser device comprises a laserhead 3, a glass window 4, a water chamber 5 and a nozzle 6. Laser beam 7emitted by the laser head 3 is focused in the nozzle 6 through the glasswindow 4 on the water chamber 5. The water chamber 5 is pressurized toallow a water jet 8 to be ejected from the nozzle 6 and to guide thetransmission of the laser beam 7 to the outer circumferential surface ofthe PCD film 2. The pressure of the water chamber is 2-4 MPa, and thediameter of the water jet is 20-50 μm. The grinding wheel is offset by acertain angle that is equal to a desired rake angle (for example 30°) ofthe micro-grinding unit 9, to form the first single microgroove 10. Themicrogroove 10 has an axial length, for example 12 mm, that is equal tothe thickness of the grinding wheel. In an embodiment, the microgroove10 has a circumferential width of 20 μm, a depth of 500 μm and adepth-width ratio of 25. During the processing, relative movementbetween the water jet 8 and the wheel hub 1 is changed to create themicrogroove 10. The grinding wheel is indexed. When the processing ofthe first single microgroove 10 is finished, the outer circumference ofthe PCD film 2 is rotated over, for example 100 μm, i.e., acircumferential width of a micro-grinding unit 9, to carry out theprocessing for the next microgroove 10. Upon the completion of thesecond microgroove 10, the micro-grinding unit 9 is formed between thefirst and the second microgrooves 10. Then the micro-grinding unit 9 isprocessed to form a clearance angle 13, for example 40°. Theseprocedures are repeated to continue to process the PCD film so as toform a number of microgrooves 10 with high depth-width ratio and anumber of micro-grinding units 9 on the entire circumferential surfaceof the PCD film 2. The formed micro-grinding units 9 have substantiallythe same shapes and dimensions. The details about a water-jet guidedlaser device may refer to Yaowen W U et al. (Overview on the developmentand critical issues of water jet guided laser machining technology,Optics and Laser Technology, 137 (2021), 106820), Yi S H I et al.(Texturing of metallic surfaces for superhydrophobicity by water jetguided laser micro-machining, Applied Surface Science, 500 (2020)144286) which are incorporated herein by reference.

The PCD film 2 on the wheel hub 1 is finally processed with orderedarrangement of the microgrooves 10 and the micro-grinding units 9, asshown in FIGS. 1 and 2. A pickling treatment and ultrasonic cleaning indeionized water for 15 min may be further performed on the grindingwheel.

The outer circumferential working surface of the grinding wheel isprovided with a large number of micro-grinding units with positive rakeangle, which ensures that the micro-grinding units are worked in apositive rake angle during grinding, lowering the grinding force ratioand temperature, effectively reducing the damage to the surface andgreatly improving the grinding performance and efficiency.

A large number of microgrooves with high depth-width ratio are providedon the outer circumferential working surface of the grinding wheel,which greatly improves the chip-holding space. Meanwhile themicro-grinding units are orderly arranged so that ordered chip-removingchannels are formed during grinding, which greatly improves thechip-removing capacity and makes the grinding wheel less prone toblockage, effectively promoting the entering of the grinding fluid intothe grinding zone, significantly improving the cooling effect for thegrinding zone, reducing the thermal damage to the workpiece surface andfurther enhancing the grinding quality.

When the micro-grinding units are processed by the water-jet guidedlaser technique, the laser beam propagates along the water jet in atotal reflection. During the processing, the laser is guided by thewater jet to the surface of the PCD film to ablate the PCD film, and theablated PCD film is carried away by the water jet. Additionally, thewater jet also cools the surface of the PCD film, which effectivelyprevents the graphitization of the micro-grinding units, providingbetter grinding performance and greatly enhancing the surface quality.

The service life of the grinding wheel is extended. The PCD film on theouter circumferential surface of the grinding wheel is deposited by theHFCVD technique. The micro-grinding units are a part of the PCD film,which prevents the micro-grinding units from singly falling off due toexcessive or concentrated grinding force and significantly improves theservice life of the grinding wheel.

The number of effective cutting edges per unit area is increased andalleviates the periodic vibration during grinding. The micro-grindingunits have the characteristics of high protrusion and good consistency,so that the cutting edge of each micro-grinding unit can participate inthe grinding.

The shape and dimension of the micro-grinding units on the outercircumferential surface of the grinding wheel both have a goodperiodicity. Therefore, in the preparation process, the relative motionrelationship between the Laser-Micro jet device and the grinding wheelcan be controlled by the numerical control technology, which greatlyreduces the difficulty in the preparation of the grinding wheel andlowers the cost.

It should be understood that the above embodiments are only illustrativeof the invention and are not intended to limit the invention. Inaddition, various equivalent modifications and changes made by thoseskilled in the art without departing from the spirit of the inventionfall within the scope of the invention as defined by the appended claims

What is claimed is:
 1. A grinding wheel, comprising: a wheel hub; apolycrystalline diamond (PCD) film; a plurality of micro-grinding units;and a plurality of microgrooves; wherein an outer circumferentialsurface of the wheel hub is deposited with the PCD film; the pluralityof micro-grinding units and the plurality of microgrooves are orderlydistributed on a whole outer circumferential surface of the PCD film;the plurality of micro-grinding units form a part of the PCD film; andthe plurality of microgrooves are spaced apart by the plurality ofmicro-grinding units; each of the plurality of microgrooves and each ofthe plurality of micro-grinding units both have an axial length equal toa thickness of the grinding wheel; the micro-grinding units eachcomprise two side surfaces and an outer surface; the microgrooves eachcomprise two side walls that form one of the two side surfaces of twoadjacent micro-grinding units, respectively; and the micro-grindingunits each have a rake angle that is positive.
 2. The grinding wheel ofclaim 1, wherein the rake angle is 10°-40°.
 3. The grinding wheel ofclaim 1, wherein the micro-grinding units each have a clearance angle of20°-50°.
 4. The grinding wheel of claim 1, wherein the micro-grindingunits have substantially the same geometric shapes and dimensions. 5.The grinding wheel of claim 1, wherein a thickness of the PCD film is1-2 mm.
 6. The grinding wheel of claim 1, wherein each of themicro-grinding units has a circumferential width of 80-150 μm and aradial height of 500-800 μm
 7. The grinding wheel of claim 1, whereineach of the microgrooves has a circumferential width of 20-50 μm, adepth of 500-800 μm and a depth-width ratio of 10-40:1.
 8. The grindingwheel of claim 1, wherein the wheel hub is made of titanium alloy. 9.The grinding wheel of claim 8, wherein the wheel hub has a diameter of100-200 mm and a thickness of 6-20 mm.